Friction article



Nov. 14, 1961 s. K. WELLMAN 3,008,224

FRICTION ARTICLE Original Filed March 26, 1956 5 Sheets-Sheet 1 IN VEN TOR.

KWHLMAN ATTORNEY Nov. 14, 1961 s. K. WELLMAN FRICTION ARTICLE 5 Sheets-Sheet 2 iglnal Filed March 26, 1956 FIG. 2

INVENTOR. SAMUEL K. WELLMAN RY fiflafl m ATTORNEY NOV- 14, 1961 s. K. WELLMAN 3,008,224

FRICTION ARTICLE Original Filed March 26, 1956 5 Sheets-Sheet 3 INVENTOR. 4 SAMUEL K. WELLMAN mwmmwalwm ATTORNEY Nov. 14, 1961 s. K. WELLMAN FRICTION ARTICLE 5 Sheets-Sheet 4 Original Filed March 26, 1956 FIG. 7

FIG. 5

INVENTOR. SAMUEL K. WELLMAN YFM 2:, 7mm

FIG. 6

ATTORNEY 3,008,224 FRICTION ARTICLE Samuel K. Wellman, Cleveland Heights, Ohio, assignor to The S. K. Wellman Company, Bedford, Ohio, a corporation of Ohio Original application Mar. 26, 1956, Ser. No. 573,708, new Patent No. 2,927,015,'dated Mar. 1, 1960. Divided and this application Apr. 7, 1958, Ser. No. 726,848 1 Claim. (Cl. 29-1825) This application is a division of my copending patent application Serial No. 573,708, filed March 26, 1956, now U.S. Patent No. 2,927,015, granted March 1, 1960, and the invention relates to improvements in iron powder and articles made therefrom and has particular significance in connection with friction composition products comprising articles of a novel low density iron powder.

Substantially pure iron powder has a wide variety of present-day uses being, for example, useful for the ultimate production of sintered predominantly metallic friction facing articles for brakes, clutches, automatic transmissions and the like.

Pure iron does not exist in nature. Substantially pure iron having less than several percent of impurities such as oxide and carbon can of course be produced by man and machine, but all substantially pure iron powder that has been known has been characterized by what I consider to be a relatively high density. That is, it is not a soft powder capable of containing a high percent of non-metallic additive as required and of then being pressed at low molding pressure (e.g., at 12.5 t.s.i.) and then sintered to form a structural part strong enough for some applications. As. an example, friction facings of sintered predominantly metallic powders have in the past had to be bonded to solid metal backings because the prior art facings were too brittle to stand the force of rivets or otherwise to be regarded as structural parts in and of themselves. This is largely due to poor characteristics of the powders and articles made from them as regards such desiderata as high compression ratio, low molding pressure, good green and sintered strength, high ultimate hardness and proper final density, to adequately protect the article against breakage and chipping both during manufacture and during use.

While it has long been known how to produce iron powder by reducing iron oxides, either natural oxide ore (Fe O or mill oxide known as mill scale (Fe O by heating in the presence of a reducing agent, either gaseous or in the form of a solid such as graphite, charcoal, coke or coal, the practice of such processes have heretofore resulted in a product unsuitable for many applications and such processes have been attended by great expense of materials and of labor and by non-uniformity of results, both as between batches and within any single batch. According to one method, sometimes known as the Chinese method, a mixture of ore, coal and coke is enclosed in small diameter clay tubes which are surrounded by fuel which is set afire and burned for several days to accomplish reduction. Then the tubes are broken and the reduced iron separated from the clay, an expensive procedure resulting in a relatively high density product, as the words low and relatively high are hereafter explained. In an alternate Swedish process, iron ore is packed in alternate layers with coal and coke in cylindrical containers which are then placed in a furnace where hot gases are passed over them to accomplish the reduction. There still remains the problems of charge density and removing the charge from the containers which are not then usually suitable for re-use, and there have heretofore also been additional problems related to lengthy time requirements, inordinate manpower requirements, and to other factors contributing to the expense of the 33 083224 Patented Nov. 14, 1961 prior art processes and apparatus, to surface oxidation of the reduced charge during cooling, to non-uniformity of results both throughout a single charge and with successive charges, to impurity and brittleness (hardness) of any powder produced, and to consequent difliculties in further processing, either during grinding or during or after mixing, molding and heating powders to produce friction facings.

The metallic product formed by the reduction of iron oxides at temperatures below the fusion point of iron is well known and commonly called sponge iron. That which I presently propose is a sponge iron product but it has a density lower than that of such products as heretofore known, which prior products may therefore now be referred to as of relatively high density.

One difficulty with most metallic powders produced according to the prior sponge iron art has been that after subsequent compression (with or without sintering) they have not resulted in articles of very great structural rigidity and have lacked other desired properties. For example, friction materials used for lining facings in brakes, clutches, automatic transmissions, and the like must be selected and compounded with many factors in mind if customer acceptance and satisfactory operation are to be assured. These factors include, among others, magnitude of the coefiicient of friction, cost of the materials and of their compounding and assembly, wear of the friction material, wear of the surface which the friction material engages, noise or quietness of the material in operation, change in the magnitude of the coeflicient of friction with changes in applied pressure, or in temperature, humidity, or relative speed of the engaging parts. Of particular importance is the cost of fabrication and this involves consideration of whether or not flat solid metal backing material (additional to basic curved or flat members such as brake shoes and clutch plates) must be provided.

While, of course, organic linings, as of asbestos, may be riveted directly to a curved member such as a brake shoe, such organic materials are characterized by a relatively high wear rate and by some fading due to a rapid succession of stops, or due to the presence of oil, grease, moisture, or high temperature. Sintered predominantly metallic friction facings made by mixing ingredients in powder form, pressing the mixture to form a briquette and heating the briquette to sinter the same have already been used extensively in industry, and in clutches and brakes for military vehicles, large trucks and buses, earth moving machinery and the like, but have had high initial cost, and other dis-advantages making them heretofore not always acceptable for pleasure car brake linings.

By way of further explanation it may be stated that while it is quite feasible to make many an article (e.g., a door handle) from almost any iron powder used alone and the article will have strength sufiicient for its intended purposes, for other applications (e.g., for predominantly metallic friction facings) it becomes necessary to use high amounts of filler (such as graphite) for lubricating or wear or even frictional properties. With prior iron powders as heretofore produced and supplied it has been impossible to use desirably high amounts of filler and still have adequate strength of finished article.

It is an object of the present invention to provide simple and inexpensive means for overcoming the above mentioned difiiculties.

Other objects and advantages will become apparent and the invention may be better understood from considera tion of the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a sectional elevation of a heating pit furnace containing a charge can or retort adapted to be used in accordance with one aspect of the present invention;

FIG. 2 is an enlarged elevation in section and taken at right angles and of a bottom portion of the arrangement of FIG. 1;

FIG. 3 is a plan iew of the pit and retort of FIG. 1;

FIG. 4 is a cross-section of the retort'can and taken FIG. 8 is a tabular representation of comparativephysical properties of prepared, purchased, and oiIered iron Powders and characteristics of articles made from some of them, the powder indicated at A. being prepared according to the present invention. a

Referring now to FIGS. 1 and 2, there is shown an iron oxide reduction retort and retort receiving pit, the.

latter comprising a part of an excavation lined with concrete 10. For reasons of economy it is often desirable. to have a single excavation contain a'plurality such as nine or eighteen retort receiving enclosures 11a, 11b, etc", of Which,as shown in the drawing, 11a is an outermost hole. Each such hole is formed as a circular enclosure by insulating wall blocks 12 of refractory material and resting upon base. blocks 13 which may be ordinary fire brick, i

As most clearly seen in 'FIG. 2, the base blocks 13 rest upon a concrete foundation 14 which in turn rests upon earth 15a (FIG. 2) or other supporting means. If

desired the outer pit walls 10 may also be surrounded by earth 15b which then serves as a good insulating medium. As shown in the drawings, a layer of heat resisting refractory concrete 16 intervenes between the: pit wall blocks 12 and the outer, or ordinary oncre e 10. A fuel and air' inlet tunnel or duct 17 lined with sheet metal 18 is provided through a portion of the outermost con.- crete 10 and through the bottom blocks 13 and at least one pipe 19 extends through this tunnel. While of course other arrangements could be used instead, in FIG. 2

three such pipes 19 are shown and it may be assumed that each pipe serves one retort enclosure location.

A cast refractory cover, 20, which is in general square at its outer limits and provided with a central annular opening 21, rests upon the top of the blocks 12 with its central opening 21 being provided for reception of a crucible can or retort indicated generally at 22 (see FIG. 1). In order to provide for heat expansion of each large block 20, adjacentblocks (e.g., 20 and 2%) are separated by a compressible compound 23 which is also provided between each outermost block 20 and the adjacent heat resisting concrete 16. V

At the bottom of the furnace at each retort location, one of the pipes 19 is connected to a bottom burner which terminates in a burner screen 31. The burner extends into a burner chamber containing a four armed spider or pedestal 32 which serves to distribute the flame and build up incandescence without melting the burner or screen. Further up, a burner tunnel 33 of refractory material (square at its outer periphery but annular at its inner) rests partly upon the spider 32 and partly upon and within adjacent base blocks 13. .Above the burner tunnel 33, and within the furnace opening lira-four pier blocks 34 of cast refractory support a disc shaped lower clay pedestal tile 35 (which serves to distribute heat to the sides) and an upper claype'destal'ftile 36 which'serves as a heat resistant support for the retort can 22. a

The retort can 22 comprises a long outer cylindrical shell 38 of a heat conducting high temperature resisting metal such as Inconel (80% Ni, 13% Cr, 6.5% Fe) secured as by welding to an Inconel shell bottom 39 which rests upon the pedestal 36 when the retort is in place in t furnace. Inside the retort can thus formed a layer of loose graphite 40 (preferably granulated) is placed upon shell bottom 39, and an Inconel bottom plate 41.

(having an OD. smaller than the ID. of the shell) is placed within the shell and upon this layer. A cylindrical expansible assembly temporarily held together (that is, until heating) is placed upon the bottom plate 41, and, in the arrangement of FIGS..1, 2 and 4, this assembly comprises three arcuate plates 42 which may be of Inconel and which are overlapped at their: ends and temporarily held together in cylindrical formation by a combustible tube of cardboard'43, although a combustible adhesivev tape, or yieldable metallic clamps or other temporary restraining means could be used' insteadi The inner diameter of the assembly of plates may be coated with graphite. The outer diameter'of the cylindrical forma tion is considerably less than theinner diameter of the shell 38, andfas shown in the drawings the cylindrical formation is centered within the shell and the intervening space between the cardboard and theshellis filled with a loose graphite. (preferably ground and granular rather, thanflake) nearly to the top of the cardboard. Charcoalfmight be used here instead of graphite, butin any event some loose carbonaceous material is provided so that when the .ichargeexpands during reduction'it' will not jam inside the outer can but, instead, there wi llfbe permitted easy extraction of the log (as the charge is called after it is reduced) so' that the (an may be. used again. V

' The cylindrical formation of overlapped arcuate liner plates or segments 42 forms an inner can which is' filled with a charge 45to be reduced and which, as in general 7 practice in the. past, may comprise a mixture of powdered red iron ore (Fe O f) and charcoabor mill'scale 1e 0,

adequate limits in this regard are generally maintained and charcoal, and in proportions such that theoxide will be reduced and the carbonaceous material will be consumed in the'process. Asjan'example', I have had good results using for the charge 1.8 ,Fe 'o, and 17% n ch malv.

' When" 's desired to commence operation with mill scale, it is preferable to obtain dry mill scale and scalp the sameqto remove any foreign'rnaterial such'as gravel,

sticksor' paper, and then mix i t with the powdered charcoall The mill scale is preferably in a dried form to prevent balling up. of the material, wetting of the charcoal, and'subsequentnon-uniformity of distribution throughout, the entire reduction .mix.

which is important in order to obtain reduced iron logs of maximum weight. Of course with the. charcoal, and with the mill scale as well, it is desirable to have a minimum variance in chemical and physical properties but by the commercial suppliers of such ,materials.

The materials are Well mixed together, as for example in a ball roll mixer or by using a conical tumbler'or' double cone blenderfor something like 60 minutes with additional mixing time being required if a laboratory analysis then indicates an unequal distribution, of charcoal throughout the blend. 7 i j From FIGS. 1, 2 and 4, it will be seen that when the charge is in place, it is separated from the outer shell.

38 of the can first by the segmented sheet metal cylinder made up of liner plates 42, second byJthe cardboard cylinder 43, and finally by the layer of loose graphite 44.

A top sealing cover is pushed down on the charge and, as shown, this cover'comprises an inner annular vent pipe 48 secured to a top cover bottom plate .49 which in turn is secured to a top cover outer cylindrical shell 50. These pieces may be made of Inconel and they are rigidly secured together as by Welding with the outer shell 59 extending above the bottom plate to'form" with the bottom plate and the inner vent pipe an annular opening. The shell 50 also extends below the bottom plate to form a depending skirt portion 50d whichispushed-down'.

into the loose graphite to lengthen the path which any Dryness also in- I V sures close packing of the reduction mix during loading gases would have to traverse to get into or out of the charge from around the outside. The vent pipe is provided in order that gases resulting from reduction of the charge may escape, and the annular opening between the vent pipe and the outer wall is filled with a castable insulating concrete such as Firecrete or other refractory of insulating material 51, such as Sil-O-Cel which is a proprietary name for a diatomaceous earth composition, exact contents of which are unknown to me but the composition is readily obtainable by this name and is characterized by good heat insulating properties and light weight. The cover as above described effectively seals against normal gas pressure from within the retort while allowing means for pressure relief in the event of blockage of exhaust lines, and it is characterized by easy attachment and removal. The refractory '51 may be cast as it is placed within the annular opening and then covered by a top plate '52 which may be of asbestos and provided in order to prevent dusting.

The outer shell 38 of the retort can 22 is provided near its top with lifting means which in the illustrated embodiment (FIG. 1) take the form of a metallic ring 53, and the assembly of retort, its charge, and its cover just described, is lifted thereby, and preferably with a mechanical hoist (not shown) whenever it is to be moved into or out of the retort enclosure 11a, the length ofthe can and the lengthof the enclosure being so selected and designed that a top portion of the can (including the lifting means) is well out of the enclosure and therefore not apt to be weakened by the heating.

Assuming, for purposes of description, that a solid log can 22 (FIG. 1) is first to be lowered into pit enclosure lla, and then filled while in place therein, the outer can (shell 38 and bottom 39) is lowered into the pit by a crane and special tongs designed to catch and hold beneath the rim 53 welded on the top outer diameter of the retort can, and after the can has been lowered into the pit a few scoopfuls of graphite are poured into the can to form a layer of graphite 40 approximately /2" thick on top of which is then placed a & thick circular bottom liner plate 41. Plate 41 may be graphite coated to prevent sticking. Next, three rolled A thick steel arcuate liner plates 42 whose inner wall surfaces have been coated with graphite may be overlapped around a steel mandrel (not shown) and the overlapping edges clamped as by the cardboard cylinder 43. The thus formed hollow cylinder is removed from the mandrel and lowered into the retort can until it rests on the-plate 4 1 and is centered. Some graphite 44 is then poured into the open space between the cylinder 43 and the outer wall 38 of the retort can to keep the liner plates and cardboard cylinder centered during the addition of the reduction mix. Reduction mix 45 is slowly poured inside the cylinder formed inside the plates 42 until the level of the charge comes within an inch or so of the top of this cylinder. The top or seal can (48-52) is then lifted, by means of a crane hoist for example, and lowered into the retort can until its bottom 49 rests on the top of the liner plates, the bottom skirt of the can sliding into the open area between the liner plates and the inner walls of the retort can. Additional graphite 44 is then poured into the open space between the outer wall 50 of the top can and the outer wall 38 of the retort can until the graphite comes within approximately one inch of the top of the can.

The gas is then turned on and lighted, the charge brought up to temperature and held there for a sufiicient time (as may have been determined experimentally from prior runs), then the gas turned off, the retort can removed, allowed to cool (preferably in a controlled nonoxidizing atmosphere), the cover removed, and the charge removed, then cut up and ground to produce the desired iron powder.

Of course, the process steps just described can be altcred. For example, it may be found easier, to fill the retort crucible 22 outside the retort enclosure, and it is not necessary to use a mandrel for the arcuate plates if a cardboard cylinder is used as their temporary binding means because after the bottom layer 40 of graphite is placed within the outer shell and the sheet metal plate 41 disposed thereon, the cardboard cylinder 43 may be put in next, then the graphite 44 poured in between cardboard and outer shell, and then the segments 42 placed within the cardboard, and then the charge dumped into the inner shell thus formed by the segments. But in any event, it is contemplated that the segmented shell of pieces 42 will merely rest loosely upon the bottom plate 41 so that it is free to move with respect thereto as the charge expands during reduction.

Alternatively the gas may be turned on and the furnace kept hot all the time, and, whenever it is desired to commence heating a particular charge, the charge in a completely assembled retort can may then be lowered by means of a crane hoist into the heated hole until approximately th-ree quarters of its length is lowered into the hole. It may then be held suspended in this position for five minutes to permit a slow overall heating up period for the can and charge, preventing a cold surface from coming into intimate contact with the hot bottom refractory plate 36 thereby to minimize danger of cracking and to increase the life of the parts, as well as to prevent a too rapid evolution of gases within the charge since the entrapped gases if evolved too rapidly would tend to cause a blowing out of the graphite packing filler. After such a five minutes suspension and preheating period, the can is lowered into position and comes to rest on the bottom refractory furnace plate. In this position the can is allowed to remain at a temperature which is suitable, for example 1810 F., and for a time which is suitable, e.g., for 72 hours or until there is a substantially complete reduction.

The retort can may then be removed by crane hoist and hooks and set in an area reserved for the cooling of cans and at this time a freshly charged can may be inserted into the emptied hole. When can and charge have cooled to room temperature and top seal can then removed, the charge may be dumped, or, if it sticks within the liner plates, a long screw hook (not shown) may be turned into the iron log and the iron log thus drawn out of the can, the liner plates pulled away, and as a final step the completed log is ground to a powder.

7 Preferably the retort is heated during operation not only by the bottom burner 30 already described, but also by a ring of circumferentially spaced burners 54 (FIG. 1) located somewhat near the top of the can. For the retort location 11a there are six of these peripheral or ring burners 54 each fed by a different conduit 55, with the six conduits 55 tapped off a top ring burner manifold 56 which in turn is fed with the proper mixture of fuel and air from a ring burner manifold feed conduit 57. Each top block 20 is, preferably at the time of its casting, perforated by six conduit receiving holes or slots 58 to accommodate the downwardly extending burner conduits 55. The burners 54 themselves may be directed downwardly as shown and in order to avoid local overheating, I prefer to provide small diameter holes 59 in each burner pipe somewhat back from the extreme end of the burner and in such manner that these will allow gas to be forced out in several directions, where it is ignited to give very good heat distribution within the pit and eliminate local hot spots.

In the arrangement of FIG. 1 a grating 60 is provided over the top end of the ventilating duct '17 and through this grating air may flow (or be forced) to follow, for example, the direction indicated by the arrows 61 to provide pit ventilation.

Meanwhile, a mixture of fuel and air is forced in the direction of arrows 62 to supply the bottom burner 30 and after ignition by some conventional means (not shown) heat therefrom follows in the direction indicated by arrows 63, that is upward and out between the can outer wall 38 and the inner circumference 21 of the top block 20. Meanwhile a similar mixture of fuel and air is forced in the direction of 'arrows 64 through the feed conduit 57 to the ring conduit 56 and down to the ring burners 54 where, after ignition by some conventional means (not. shown) heat'is produced and the exhausted products of combustion eventually turn upward and also discharge out between the-can outer wall 38* and; the inner circumference 21 of'the top block.

Thus, and while electric or some other heating mea might be used instead, as above described the mill scale and .ground charcoal aregas-fire heated in a closed (and graphite sealed) metal cylinder and this will produce carbon dioxide (CO and carbon monoxide (CO) gases and a porous log of sponge iron. The by-products of reduction, that is the carbon monoxide and carbon dioxide gases, are carefully carried away as through hose-or. conduit 66 coupled to exhaust-conduit 48. They mayrthus be carried to arCOmd'll-Dl'l manifold (not shown) or, if

desired, the arrangement may be as in FIG. 7 where the exhaust conduit 48 of onecan 272a which is being heated is shown connected through piping 67 to the exhaust conduit 48of another, can 22b7-which is being cooled with the result that the can. 2212 during iskept from absorbing any atmospheric air which might tend to re oxidize the log contained therein. Since the ,cold can will not absorb as much of these .gases'aswill be evolved from the can beingheat'ed, I have also shown a lay-pass take ofi through a T fitting 68 and through a hand valve 69 to a nozzle 70 where excess gases maybe discharged 7 to and burned in the openair. Any productsof burner fuel combustionin therpit enclosure are readily discharged to the open air, or to an exhaust hood (not shown), and if they contain any dangerous CO gases it is a simple matter to either increase the air-supply to the burners or else such gases at the opening between the heated can outer wall 39' ahdtheassociated top cover 20. t Y 7 Using the arrang ment of FIGS. 1-4, and after considerable experimentation to determine optimum physical dimensions with due regard for-heat distribution and penetration and chemical analysis of the finished product,"

motorized sifter with coarse rejects being returned to the grinder, but in any event as a final product satis factorily pure'and very desirable soft iron powder is obtained.

- During operation of apparatus as above described the outer burners help assure a uniform heat distribution from the top to the bottom of the associated hole, and also tion and also for the furnace cans by eliminating burn-f outs in bottom areas as a result of overfiring at bottom in order to sufficiently heat top portions.

Thetop can serves as an eifective seal, requires little .or nounaintenance, holds up well .withrepeated usage' without cracking or buckling.

The-retort can and furnace above described provide forleasy removal ofthe retort can' from the furnace, and

include means for removing the charge without destruction ofthe, can. if :necessary thearcuateliner plates '(42) may be cleaned and rerolled to shape but I have found 7 that the liner plates are. capable of being're us'ed on an the charge, and, due to the overall design, without danger flcalsage (as of pressure outwards or air inwards), and" the final product hasa relatively low oxide, low-carbon it was found that a 310 charge could beeffectively r d e to a sohdZO p nd g of desired content in' seventytwo hours, with test results "as follows:

gt. Ultimate Oxide Carbon Wgt. of Chg, Reduced Temp, Time, Content, Content, Pounds Log, F. Hrs. Final Final" Pounds In a process of making low density iron powder according to'some aspects of the present invention, scalped (preferably) and dry mill scale and charcoal are obtained and mixed as in a rotatable cone blender, and after these materials are thoroughly mixed the blender is Stopped and emptied into a retort can (22). Next 'the can is sealed with a top cover (48-52) and conveyed to and placed in a heating pit (e.g., 11a) where heat is applied to the bottom and outside of the can, with the heating continuedfor a time sufficient to reduce the charge. Then the sealed can is removed from the pit and may be placed on an open floor where it is allowed to cool while the charge is subjected to a controlled atmosphere, forexample of city gas unless it is desired to use the waste gases from another "can beingheated (as in FIG. 7). Next the top seal can is removed and the charge is thereafter removed without destroying the can, for example by the prior employment of the liners described in conneotion with FIGS. 1, 2 and 4. The removed charge is then broken up as with an axe, if that is necessary, and next the material is ground as in a motor driven grinder, and if desired it may be further processed in a average of live to six times: before requiringreworking.

Whenliners'are used the double construction of retort can 'helps assure that there willbeno buckling, distortion or V warpage', andwith all thearrangements disclosed the can extends above the pit for cooling of the top or'lifting portion to prevent Weakness at this point (thus enabling the top to retain sufiicient strength to enableit tobear the can total weight when .it isto be liftedfroni the furnace). V "A relatively-largeweightofcharge may thus be proc- V 1 essed in a greatlyreduccd processing time, and without the priorart, disadvantages .of destruction of a part of the processing apparatus' with each run.

Proper. heat distributionis,assured'to all portions of on cntastobserved, for example, in the critical top and bottom arcasof each log :sampled and Ianalyzed, and as also indicated by dynamometer tests aftercompleted logs have been ground, molded, sintered and properly assent bled to determine frictional wear properties of varying batches from logs so produced. For such powders, mold growth, green strength, sintered strength, workability-and i iriction andwear properties were all found to be excellent and it was also found that iron reduction methods and apparatus of the. type described-produced a fernlike powderwhich, comparedwith any heretofore known, was softer and more compressible, thus giving lower costs for fabrication, longer die life, and longer wearing friction materialhavinga higher'coeificient of friction and having other advantages; apparent to those skilled inthe 'art.

' Those skilled-in the art willrecognize that the ground v powders 'may. be utilized .in the production of friction articles, suchas brake and'clutch linings made by pressing and sintering mixtures ofmetallic and non-metallic powders to provide'numerous advantages over friction linings of asbestos or other non-metallic materials in that the sintered articles are less susceptible 'to changes'in temperature and atmospheric conditions, are less affected by ex traneous oil, grease and foreign matter, and show less wear with'the same use.

To havethe best iron powder for such friction appli cations it is preferable that the powder have a low can bon content (to avoid the formation'o-f hard carbides) but any carbon not exceeding l%'seems quite tolerable and any oxide content below 3.0% is quite permissible so far as friction and wear and other properties of theultb' mate material are concerned.

It is not exactly clear why a powder which:is superior to anything known tothe prior art, results from'the use of apparatus and methods as above described. Form and purity of. the initialmaterials' is of some importance, but it is not absolutely essential that they be pure Graphite 9 instead of charcoal would probably not be suitable because its use would tend to increase reduction time cycles for same weight of charges.

Time and temperature are probably of great importance but no definite limits can be set up because each depends upon the other and because together they depend in turn on the dimensions of the apparatus and of the charge, lo cation of burners, and many other factors. Those skilled in the art will quite easily recognize, of course, that too little heat will result in an insufficiently reduced product, too much heat may cause sintering of the log and cause it to be too hard. I have found that in many cases reducing temperatures of 1700 F. took too long for the process to be economical; 1800 F. (with a certain arrangement of burners) is just right; 1850 F. produced a powder which was too hard; and 1900 F. produced a compact log resembling ordinary iron or steel.

With the arrangements above described, it is easier than ever before to provide controlled conditions (e.g., of heating time and temperature and pressure and even particle size) which will result in a desired degree of sponginess of the iron product making it well suited for the ultimate production of powder metallurgy friction articles comprising so-called iron base mixes, and they will then have characteristics quite comparable to that of more conventional (but more expensive) copper base mixes, while being far superior to copper base mixes in many respects.

That is, the retort can and furnace designs disclosed not only provide for easy removal of the retort can from the furnace, but still allow the buildup of gas pressure within the chmge during reduction (which may account for the novel product) while means are also provided for removing the charge without destruction of the can.

I have found that it lies well within the province of the mechanic after brief experience with apparatus and processes such as those described to produce a novel product having desired characteristics and characterized by an ap parent density in the range of 1 to 1.5 (gms./cc.).

Possibly the novel product is due to the use of a closed and sealed can and consequent production of some gas pressure therein, though even in the Swedish process there is undoubtedly some gas pressure produced between the alternate layers of coal and coke. However, neither the products of producers of Swedish type nor the producers of other so-called low density powders seem able to achieve an apparent density less than 1.59 and throughout the world all producers of the so-called low density powders (with the single exception of applicants company resorting to his invention) have to employ an added (and expensive) gaseous reduction following sagger (solid reducing agent) reduction to get oxide content below 10%.

In an effort to dispense with cost of development if suitable powders were already available, I established contact with the worlds foremost producers of iron powders and these contacts indicated that commercially available iron powder would just not do the job desired to be done as well as powders made according to apparatus and processes described in the present application.

Referring to FIG. 8 there is there shown comparative physical properties of prepared, purchased and oifered iron powders, where the properties listed in column A are those of powders, compacts and sintered articles made from such powders prepared by applicant according to his processes, those under column- B are for powders from supplier B, those under column C for powders of supplier C, and so on, there being two columns for each of E, F, and G to show comparison of suppliers data and local tests made upon powders from each of these sources. In some cases suppliers data was found not to be available to me, and in other cases data furnished by suppliers quickly indicated that local tests would be quite unnecessary.

Possibly the most important figures in the Table of 'ing pressure.

FIG. 8 are those for apparent density. Such density was measured by a Scott Hall flowmeter in a manner well known to those skilled in the Of course this factor of apparent density must be considered only in connection with consideration of particle size distribution. In general, a fine powder is desired but finer powders can be obtained only by grinding, or selective screening. Selective screening is not usually economicard).

The full significance of apparent density becomes apparent when subsequent molding is considered. Low apparent density gives low pressed density at low mold- Of course particle shape has to be considered for even a hard powder might be used to produce an article of low pressed density if the pressed article were provided with many pores, but I am talking about a homogenous, imperforate, substantially solid pressed article, i.e., one substantially free from noticeable voids or one whose apparent porosity is less than 30% of total volume. Low apparent density also gives a high compression ratio, and while the compression ratio seems to depend to some extent on actual molding pressure, height of fill and size of compact, it should be apparent from the table that with applicants powder there is a high compression ratio even at the very moderate (and therefore preferred) molding pressure of 12 /2 tons per sq. in., a pressure lower than that recommended by any of the suppliers (even though resorted to by one of them when proceeding at applicants direction).

Considering the properties listed under horizontal subtitle 2 (for green molded compacts) although the green hardnesses are comparable for the various powders, the green (pressed) density of the A powder was the least and, of more importance the green strengths of compacts made from this powder was, because of the higher compression ratio (i.e., better compressibility) by far the highest though this last mentioned factor could be found only by handling compacts and noting breakage and could not very well be tabulated in numbers.

Attainment of high compression ratio with the desired low molding pressure permits maximum strength of green compacts with minimal pressing equipment.

Through experience of applicants company it has been found that only the A powder can be molded automatically because only the A powder lends itself for automatic operation at low pressures. Using such a low density, high compression ratio powder increases life and reduces wear of dies, die walls and press itself. Whereas at the present day it is prohibitively expensive to order a press big enough to proccess other powders, with the A powder existing press equipment (for example that already built for copper base mixes) can be used for making iron base friction materials because applicant has found that with powder made according to the invention he can mold excellent iron base sintered friction facings at the very low pressures of 12.5 tons per sq. in., as contrasted with the 25, 30, 50 or even tons per sq. in., as heretofore used.

Of great importance is the fact that the new iron powder, because it is so much softer, greatly facilitates the formation of a friction article substantially entirely a pressed and sintered mix of iron and graphite, or car- 11 bon. articles (ash trays, etc.) could be made with iron 01 other metal and little filler, wherever substantial amounts of a filler such as graphite is required (as for pressed ands-intered metallic friction facings) the new apparatus, processes, powder and articles of the invention permit use of high amounts of such filler while permitting processing equipment of minimum cost vandfinished articles of requisite strength.

While I have described particular embodiments, various modifications may obviously be made'without departing from the true spirit and scope of my invention which I intend to define in the appended claim.

I claim: I Y I A compacted and sintered friction articlehaving as its base an iron powder of apparent density of, 1.0 to 1.5

grams per cubic centimeter for a screen analysis in which not more than 35% passes through a 325' mesh screen, at least about 5% remains ona 325 mesh/screen while capable of passing through a 250 mesh screen,

atleast about 5% remains on a 250 mesh screen while capable of passing through a 200 mesh screen, at least about 15% remains on- 21200rnesh'screen while capable As mentioned in the beginning, while many old V 12 of passing through a 150 mesh screen, at least about 15% remains on a 150 mesh screen while capable of passing through a 100 mesh screen, at least about 5% remains on a 100 meshscteen while capable of passing through an 80 mesh screen, and not more than 1% remains on an 80 mesh screen, the balance of said article being friction modifying material. References Cited in thetfile of this patent V UNITED STATES PATENTS OTHER REFERENCES Symposium on Powder Metallurgy, Special Report No. 38, 2d edition (revised), December 1947, published by the Iron and Steel Inst, pp. 27-34. V 

